Press brakes are employed to bend metal sheets into desired configurations. A press brake commonly is equipped with a lower table and an upper table, one or both of which are moveable to close the tables upon a workpiece positioned between the tables. Forming tools are mounted-to the tables so that when the tables are brought together, a work piece between the forming tables is bent into an appropriate shape. The upper table commonly includes a male forming tool having a lower work piece-deforming portion of a desired shape, such as a right angled bend, and the lower table commonly has an appropriately shaped and aligned die, which for example may be V-shaped and open upwardly to receive the work piece-deforming portion of the upper tool. A metal sheet positioned between the tool and die thus is pressed into a desired shape. Forming tools and dies commonly are horizontally elongated so that work pieces of various widths can be accommodated.
It is often necessary to exchange forming tools and dies to accommodate different bending operations. The dies, commonly resting on the lower table of a press brake, are readily removed and exchanged for others. The forming tools that are mounted to the upper table of a press brake often are not so easily replaced, however. Tool holders that are carried by the upper table commonly make use of a clamp that clamps upon an upwardly extending tang of a forming tool to hold the tool in the holder.
Tool holders and tools may have respective interlocking safety keys and key-receiving grooves to restrain accidental dropping of tools once the clamp of the holder has been loosened. Forming tools can in some instances be removed downwardly from the holder once the clamp is loosened, and in other instances the forming tool must be removed by horizontally sliding it from the holder. If a forming tool of some length (and hence of some substantial weight) is to be replaced, it sometimes is difficult to slide the forming tool horizontally from its holder because of the proximity of neighboring forming tools which may themselves have to be removed in order to complete the tool exchange process. Because long forming tools can be quite heavy, when a clamp is loosened to the point that the tool can be removed by moving it downwardly, care must be taken to prevent the tool from slipping from the tool holder and falling.
Various press brake tool holders have been devised in an effort to facilitate the exchange of one forming tool for another. Examples of the tool holders of this type are shown in U.S. Pat. Nos. 5,513,514, 5,511,407 and 5,572,902. More recent tool holders are described in U.S. Pat. Nos. 6,003,360, 5,245,854, and 6,467,327.
U.S. Pat. No. 5,619,885, the disclosures of which are incorporated herein by reference, shows a press brake tool and tool holder in which the tang of the tool is provided with a vertical sliding surface that slides against a vertical surface of a plate of the holder. The reverse side of the tang is provided with a slanted planar surface that diverges downwardly from the vertical surface. The holder and tool also have engagable, generally horizontal, force-transmitting surfaces for transmitting vertical forces between the upper table and the tool. The slanted surface of the tang is designed to come into surface-to-surface contact with a clamp element of the tool holder when the tool is pushed upwardly into the holder. Because of this slanted configuration of the tang, the clamp of the tool holder is forced open when the tool is forced upwardly between the plate and clamp. As the tool is pushed upwardly, a lip on the clamp engages a safety-groove formed in the tool. The force exerted by the clamp upon the tang has a horizontal component to clamp the tang against the vertical surface of the holder plate, but this force also has a downwardly directed component. Clamps and tools of this type generally are known as “Amada style”, and are commonly sold under the trademark “One Touch”. U.S. Pat. No. 6,003,360, assigned to the assignee of the present application, shows a tool holder manufactured by Wilson Tool International, Inc. and sold under the registered trademark “Express®”. Note should be made that the tangs of the press brake tools described in this patent are exemplified as being generally rectangular in cross-section, as compared to the generally wedge-shaped or slanted tangs of the Amada-type tools shown in U.S. Pat. No. 5,619,885.
Other Press brake tools and tool holders are shown in U.S. Pat. Nos. 6,138,492 and 6,557,390, both of which are assigned to the assignee of the present invention. See also U.S. Pat. No. 6,564,611. A summary of certain types of press brake tools and tool holders is provided in U.S. Pat. No. 6,467,327, the contents of which are incorporated herein in its entirety by reference and which describes “American” style tool holders and tools.